442 Mr. Herapath on True Temperature, and the [Dec. 



Places of observation. 



„ . ,, „ , 'Temperature 



" e ^ ht0 f the of ebullition 

 barometer, i c 

 „ ,. , . ' i of water in 

 English m-j Fahr 



ches - Luc. 



Beaucaire 



Geneva 



Grange Town . 

 Lans le Bourg . 

 Grange le F . . . 



Grenairon 



Glaciere de B. . 



Temp, in Fahr. 

 by Dalton, the 

 tensions being the 

 same as De Luc's 

 barometric pres. 

 sures. 



30-105 

 28-835 

 26-122 

 25-732 

 25-673 

 21-770 

 20-971 



212-83° 



210-49 



205-50 



205-65 



204-71 



196-84 



195-26 



212-50° 



210-34 



205-33 



204-56 



204-45 



196-51 



194-75 



Excess of temp. 

 Ebullition above 

 temp. Temper, 

 tension in Fahr. 



+ 0-33° 

 0-15 

 0-17 

 1-09 

 0-26 

 0-33 

 0-51 



If any corroboration of the simple conclusion I have drawn is 

 wanting, the numbers of the present table, if correct, afford it. 

 Philosophers, however, have been so accustomed to confound 

 the temperature of tension with that of ebullition, that it is 

 become habitual to consider them as one. Into this error it 

 seems Dr. Wollaston has fallen. This gentleman has presented 

 two papers to the Royal Society, describing an instrument which 

 he terms a barometrical thermometer, for measuring the heights 

 of mountains by the temperature of the ebullition of water under 

 different compressions. I have not myself read the Doctor's 

 papers, but by the accounts I have met with, he makes the tem- 

 peratures of ebullition and tension the same, and computes them 

 from a theorem given by Dr. Ure. However useful and correct 

 Dr. Ure's theorem may be for the determination of the tension in 

 the neighbourhood of 212°, it cannot, from what I have just 

 shown, take from Dr. Wollaston's method the disadvantage of 

 confounding two distinct things, and, therefore, of being itself 

 founded on erroneous principles. I shall make no observation 

 on the probable increase by such a method of the common baro- 

 metrical errors ; nor shall I enter into any discussion of the other 

 merits of the instrument. My object is merely to show that 

 whatever merit may result from any ingenuity of idea, the prin- 

 ciples of the instrument are not such as can be called correct, 

 which I have no doubt the Doctor will, on a slight perusal of 

 what I have written, immediately perceive. 



At some future period, I may describe a simple portable alti- 

 meter I have contrived, that Mr. Trimmer and myself have some 

 thoughts of making, which appears to me to possess all the 

 advantages of a barometer, and to have an almost indefinite 

 precision, with a convenient portability ; but now I am anxious 

 to say something of other matters. 



